1. Field of the Invention
The present invention generally relates to an air detector for use in an infusion device, and more particularly, to an air detector designed to detect air bubbles or columns in an infusion solution flowing through a tube from a supply bag, etc. into a human body in the medical infusion device or the like, which facilitates easy and reliable loading of said tube into the infusion device.
2. Description of the Prior Art
Prior art infusion devices of the kind referred to above include an air detector using a ultrasonic or an optical sensor for detecting air bubbles or columns in the liquid flowing through a tube. The air detector is loaded in a part of the tube.
Two types of the air detectors are known. More specifically, in the separate type as shown in FIG. 5, a signal emitting member 1 and a signal receiving member 3 of the sensor are separate components in such structure that the former is mounted on a stationary unit 2 of a pumping station, while the latter is carried by a movable unit 4 such as a door. When the door 4 is closed, a channel 6 is defined between an upper surface of the signal emitting member 1 of the stationary unit 2 and a lower surface of the signal receiving member 3 of the movable unit 4, into which a tube 5 is accommodated. Accordingly, when the movable unit 4 is closed while the tube 5 is loaded into an upper recess 7 defined in the signal emitting member 1 of the unit 2, the tube 5 is deformed into a flattened configuration within the channel 6 to provide an enlarged surface area 5a to be in contact with the signal emitting and receiving members 1 and 3.
On the other hand, in the unitary type of the air detector as shown in FIGS. 6 and 7, a tube-receiving groove 8 is defined in the stationary unit 2. Both the signal emitting and receiving members 1 and 3 are embedded in the opposing walls of the groove 8. The unitary type is mainly used for detecting relatively short air bubbles or columns and therefore the length of tube-receiving groove 8 is relatively short, exerting less resistance in contact between the groove and the tube. Accordingly, the tube may be fitted into the groove 8 by pushing by fingers.
In the above-described separate type, it is difficult to maintain a constant distance between the signal emitting and receiving members so as to stabilize the performance of the detector.
In the unitary type, it is necessary for the tube-receiving groove 8 to have a relatively narrow width in order to obtain a high sensitivity in the detector. In order that relatively elongated air bubbles or columns can be detected in the narrow groove 8, it is necessary to correspondingly elongate the inter-sensor distance in a lengthwise direction of the tube as indicated in FIG. 7. This necessarily increases the frictional resistance of the groove and makes it difficult to place the tube in the groove. In other words, when the air bubbles or columns of a size corresponding to L1 are to be detected, the inter-sensor distance between sensors 1 and 1, and 3 and 3 is necessary to be L1 as shown in FIG. 6. Meanwhile, when the air columns of a size corresponding to L2 are to be detected, the inter-sensor distance should be set L2 as shown in FIG. 7.